Category Archives: design

The back porch project

And a project it is!

We knew pretty much from the beginning that the back porch would need to be replaced. It may look sort of OK from the outside, but the bones are rather ailing.

Because it was an enclosed porch, we had planned to rebuild it as an enclosed porch. That got us into a whole lot of trouble, starting with zoning. Not only did we have to apply for an administrative adjustment because our building set backs weren’t right, but we also found out that the currently existing enclosed porch was never permitted. Setting this right rested on our shoulders. The good news is that another administrative adjustment and a $250 fee got us a permit for a new enclosed porch.


Nice porch, isn’t it? And expensive, too, as we quickly found out. We knew that we didn’t want to spend that kind of money, but still tip-toed around the issue for a couple of years. Then, our neighbors got their back porch replaced – a typical open, Chicago-style back porch. That made us realize that an enclosed back porch is more a “want” than a “need.”

We already have 1,500 square feet of living space on the 1st and 2nd floor – which is a lot for an old building like ours. Adding another 250 square feet of conditioned space seemed too much of a luxury, certainly at that price tag.

Changing plans

So, we decided to instead build an open porch, with the exception of the basement level where we can have a workshop and tool and bicycle storage. We also decided to keep the roof access to our future vegetable garden, the PV, and the Solar Hot Water panels.


We also decided to keep our options open. If we want to turn the back porch into a three season room or sleeping porch at one point, we should be able to do so. That would require us to waterproof each porch floor, but we can plan for that.

The building permit we currently have includes the porch … except that the porch we now plan on building is different from the porch on the permit plans. I hate to admit it, but we need to pull another building permit, just for the porch.

This time around I won’t have to do it, but rather we will have our porch contractor take care of it. It’s nice to have that task delegated, except that the contractor isn’t a great communicator. Let’s see where that will take us…

While we wait for the plans and permit, I have some serious prep work to do, like that old grease trap, which we temporarily turned into a sump pit.

Related posts:

Zoning surprise

Zoning – the process

Dusting off the wish list

The green roof dream

Grease trap cleaning

Nail biter


1st floor bathroom layout

Compared to today’s standards, our 1st floor bathroom is, let’s say, rather compact. It originally measured 6’ 8” by 5’ 10”.

We were keen to keep, if not improve, its functionality, and maybe even arrange the layout in a way that would create the illusion of it being more spacious than it really is.

Early on in the project, we scrapped the original sewer stack and later on replaced it with a new one in a slightly different location. Moving the replacement stack a few feet further to the west allowed us to switch the vanity and toilet around.

This was a welcome improvement as one no longer trips over the toilet while entering the bathroom.

We also were able to add about seven square feet to the bathroom space.

The north wall faced built-in shelves on the dining room side. By removing the shelf space we added 16 inches to the bathroom.

What to do with the good old bathtub?

Why should we install a new bathtub if, in the end, we ‘ll just use it to take showers? Can you remember that last time you actually have taken a bath in a bathtub? I cannot. But then, I am also a tall guy and taking a shower just seems more convenient.

Cathy and I sat on this issue for a while and eventually decided to scrap the tub in favor of a barrier free, walk-in shower.

The factor that made us lean towards scrapping the tub had to do with plumbing foresight. We positioned the shower drain such that it could be converted to a bathtub drain, should we change our minds down the road.

I have to touch on one of my favorite topics – moisture management. Seriously, while deconstructing the interior of our house, we got to see first-hand the damage improper moisture management can cause.

You can read up on our research into moisture management and basic management principles in these two posts:

The bathroom, in building science terms classified as a wet room, should have a floor drain. Yes, we already have the shower drain, but because of its location, it won’t be able to serve all of the bathroom area. Plus, the shower drain may one day be converted to a tub drain.

Adding a second floor drain was relatively easy while rebuilding the entire plumbing system. To see how we made the two floor drains work, go to the post Slippery Slopes.

Another must is to have the bathroom floor waterproofed and tiled. The same principle applies to the walls around the walk in shower. Basically, anything that gets exposed to water or water spray needs the waterproofing and tiles.

We planned on continuing the tile treatment around the bottom half of all the other bathroom walls. But at this point, its really more about aesthetics.

A recent post covered the subject of the bathroom cabinet, which we would like to add to the northwest corner.

We also will need some kind of shower enclosure. One idea was to install on a shower wall, somewhat similar to what we have in the garden unit bathroom.

But this solution would make the bathroom feel really small again – too small for our liking!

If, instead of the rigid shower wall, we would go with a shower curtain, we could borrow from the shower space whenever the shower is not in use.

This simple trick would significantly increase the perceived spaciousness of the bathroom and the ease at which one can move around.

So much for the layout and design ideas. Now it’s implementation time!

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More about space and time

A whole lot of things are happening on the 1st floor and I have difficulties keeping the blog up to date with our construction progress. That said, I began to tell the story of our architectural decisions as they relate to the floor plan, but stopped sort of in the middle – with the half bathroom, the pantry and the bedroom closets.

There is more to tell, and now may be a good time to conclude that story, before too much time passes.

The foyer and old tenant room

If you take a look at the floor plan above, you will notice a door at the end of the foyer leading directly into the 3rd bedroom. The strange thing is that the 3rd bedroom has another door leading into the dining room. A bedroom with two doors?

Eventually, it was explained to us that it was not uncommon in the early 20th century to rent a bedroom to a tenant. The door at the end of the foyer allowed the tenant to come and leave without disrupting the activities in the men’s and women’s parlor (library and living room).

Because we don’t have plans for tenants at this point but thought of turning the 3rd bedroom into a small home office, we decided to remove the door between the foyer and 3rd bedroom. That leaves us with extra space at the end of the foyer that we split into a built-in shelf on the office side and a coat closet on the foyer side.


When we viewed the house for the first time, back in fall of 2008, the 1st floor living room still had a hutch (see also floor plan above). A few months later, the scavengers got into the house and, amongst other things, had removed the hutch.

With no original hutch left, the decision to turn the space between the living room and master bedroom into the ventilation closet was an easy and logical one, considering that we were able to reuse the adjacent chimney for the ventilation exhaust.

We also must have had a hutch once in the dining room, although Cathy is of the opinion that it may have been a Murphy bed.

The question here was whether we should dedicate this former hutch space to the dining room, with a new hutch or built-in shelves, or to the bathroom, giving us a little more space to move around. Because the bathroom is very small, having an additional 16 inches of floor space did sound awfully attractive.

The china cabinet

Last but not least is a minute change, so subtle I almost forgot about it. That’s the storage closet in the corridor between the dining room and kitchen (see also floor plan above).

The northern end of the storage closet had this incredibly awkward triangular shape. With the discovery of the hutch (or Murphy bed) in the dining room, the idea emerged to turn the triangle of the storage closet into a built-in china cabinet on the dining room side.

This turned the formally dead triangle into a useful and hopefully a charming cabinet. It will be interesting to see how we will finish it.

That concludes the changes to the original floor plan of the building. As a summary, you find below a graphic of the original floor plan and a graphic with the changes described above in a previous post.


Space and time with a coating of architecture

We had a quite a time discovering the original floor plan during the deconstruction process. We mostly liked what we uncovered.

See also:

Our decision to largely restore the original floor plan was an easy and swift one. That also meant that we are stuck with the original room sizes. That is not a problem; it is just a little unusual if measured against anything that resembles today’s McMansion architecture.

Small is beautiful

Houses a hundred years ago were tailored to a different social structure then we have today. Bedrooms were small but functional – small rooms, no larger than 100 square feet for rest and sleep, sometimes with a closet and sometimes without. There was also one small bathroom – just enough space to use the toilet and get cleaned up.

The social spaces including the kitchen, dining and living rooms, on the other hand, were generous in the space they provided to the user, each measuring 200 to 300 square feet. They often were connected to each other with large, wide doors, effectively doubling the space if the doors were left open.

Would we desire a contemporary sized bedroom or bathroom, we would need to encroach into the square footage of the social spaces. This is an idea we did not feel at ease with.

The function of time and activity

We don’t necessarily spend most of our time in the larger social spaces, but they are the areas in which most of the activities takes place: Cooking, eating and resting (other than sleeping); having friends and neighbors over; having the birth, exchange and flow of ideas; observing the activities on the street and in the garden; reading and listening to music …

The 100 year old layout – the way the social spaces are sized, structured and connected to each other – is masterful. Having resources flow into changing this layout feels wasteful, while re-using the inherent charm and functionality of the original floor plan appears resourceful.

It isn’t that creating larger bedrooms didn’t cross our mind or that we weren’t tempted. But during a down-to-earth moment, we realized that we would be better off getting over the “standing in the candy store” mentality. If this is to become a green rehab project with some level of integrity and for the sake of functionality, we have to be rational and focus on the real needs, not so much the wants.

The déjà vu factor

It was helpful to think back to those bedrooms in previous apartments. They all were small rooms, around eight by ten feet, and they did the job generally to perfection. So what would be the measurable benefit of adding more square feet to an eight by ten bedroom?

To close the circle, we thought back some more: “What did we have in previous residences that did and did not work?”

Having only one bathroom could at times become tricky in a 1,450 square foot living space. Adding a very simple half bath (a toilet and a sink) made it quickly onto the “need” list. We identified the original pantry as the most suitable location for the half bath, but at the same time, identified the pantry space as a “need” item.

That problem was solved when we eliminated the third stair access into the basement and instead turned it into the new pantry, almost identical in size to the old one.

It’s down to the closet

Small bedrooms, like ours, work really well if there is little or no clutter. To prevent clutter, sufficient storage or closet space evolved into another critical “need” item on our list. Even though each bedroom came with its own walk-in closet, we were still looking for opportunities to add some storage space.

By switching the door around, the closet that formally served the master bedroom is now storage for the guest bedroom. That leaves us with two walk-in closets for this room, but none for the master bedroom.

We became comfortable taking this step as we scrutinized the relatively long and narrow layout of the master bedroom. If we shorten the bedroom by three feet, giving us the needed space for two walk-in closets, we end up with a functionally sized and better proportioned bedroom and even room for a dresser.

Isn’t it amazing how much thought goes into this and how few walls are moved as a result?


The green roof dream

A vegetable garden on our roof has been on our wish list for a while. The question is if we can pull it off.

There are structural and budgetary challenges and they are closely linked. We have some very impressive steel columns supporting an equally impressive steel beam running near the center of the basement.


This assembly supports the interior load bearing wall of the 1st and 2nd floor and appears so sturdy that I was convinced it would support a green roof.

The actual roof structure, the 2 by 10 old growth joists running across the building, did not generate much confidence. I assumed this was the weakest structural link and would not support the extra weight of the airy vegetable plots.


How much structural reinforcement is needed? Are we talking about $500, $5,000 or $50,000? To find out, we need a feasibility study from a structural engineer.

I got Kerry from Louis Shell Structures (LSS) to take a look at the house and structures with me. He was very happy that I had all the walls open. He actually could look at and measure all load bearing components, which we did for about two hours.

To accommodate the vegetable garden, I assumed a growing medium depth of 6 inches and a drainage layer depth of 2 inches. All in all, a load capacity of 80 pounds per square foot (psf).


Kerry took all this information back to his office and began to crunch numbers–a lot of numbers! Lo and behold, the results were somewhat unexpected.

What I assumed to be the most solid component, the steel columns and beam, turned out to be a weak link. And what I thought to be the weakest link, i.e. the roof joists, appeared to be rather sturdy. Almost all roof joists are fit to support the additional 80 psf, with the exception of the long span area over the dining room and the kitchen.


Over the dining room area, I will need to sister the existing roof joist with two 2 by 10s (one on each side). Over the kitchen area, I only would need to add one 2 by 10 to each existing joist. All roof joists will need vertical blocking over the load bearing wall. And that is it for the roof structure!


As for the interior load bearing wall on the 1st and 2nd floor, we need to add some minor reinforcement. All typical door openings need a new 2 by 8 double header to transfer the load.


The larger opening for the French doors has to be reinforced with a double-LVL header (2 by 9 ¼ inches).


Some of the studs in the load bearing wall do not line up with the floor joists, which prevents proper load transfer. To solve this problem, we either need to add studs, or move the existing studs under the floor joists.


Last but not least, we have the unexpected weak link in the basement. It turns out that we will need to add a 4 inch steel pipe column half way between each existing steel column. The new columns will require a 4 by 4 foot concrete spread footing.


As for the budget, I think we are probably in the $5,000 range for these reinforcements. I am not sure when we will be able to put up the green roof. What I do know is that we should take care of the reinforcement now, while we have the chance.


How to put it back together

I listed the various reasons why we wanted to start fresh with a new basement slab. I also mentioned a number of items and functions we hope to integrate into the new floor. It is time to figure out how we will put it all back together.


After some back and forth, we decided that a hydronic radiant floor heating system is the way to go in the basement. It makes sense and becomes somewhat cost effective, considering that we’ll start with a new floor slab. The system will meet the heating loads for the basement and add comfort.

Building codes, energy codes and Chicago Green Homes requirements aside, insulating a floor slab with a hydronic radiant system becomes imperative (see also Basement floor post). I already have half the insulation I need for under the slab. But that is only half the story, as I learned through my research.

I will have to create a bond break with the same XPS insulation around the entire floor slab perimeter (see detail above). It provides a thermal break to the foundation wall and prevents heat from bleeding out of the floor slab.

We will have to carefully seal the bond break at the top for moisture and radon gas control. If there is any radon, it should remain under the slab, where we will provide a controlled escape route. A system of perforated drainage pipes in the aggregate base is connected to a vent stack, helping to collect and remove any radon.

See also:EPA’s A Citizen’s Guide to Radon

Moisture control is built in at several levels. I already mentioned the seal over the bond break (see detail above). In addition, a polyethylene vapor barrier between the concrete slab and insulation prevents water vapor diffusion from the subgrade into the floor.

The aggregate base supporting the floor slab is ½ inch stone that also acts as a capillary break. The stone base prevents any water from wicking up from the subgrade towards the floor.

While at it, we also would like to include a perimeter drain along the entire interior of the foundation wall.  The purpose of this drain is to keep the footing reasonably dry. The dryer the foundation wall the less moisture will wick up and diffuse into the open basement, where it may cause condensation problems.


Basement floor

I mentioned the salvaged insulation I got for the new basement slab. Why do we need a new floor in the basement? There are several reasons.

Take a quick look at the images below. This basement floor is uneven, crumbling and has been patched everywhere. It is time to start over.

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Why not float a fresh layer of concrete over the existing floor? Our current ceiling height is 7 ½ feet and we like to keep it that way. I am 6’7” and you have no idea how good it feels to walk in a basement where you don’t have to duck. If we’d ever like to convert the basement into living space, Chicago code requires a 7 ½ foot ceiling height. We call that a pretty strong incentive to removing the old slab and start over.

Once the old, existing concrete is removed, we will have access to and can check on the sewer pipes. If any repairs are needed, this is a good time to do it.

There is no evidence of flood damage in the basement, but I suspect that the foundation walls may have a little moisture issue. A footing drain along the inside may help to solve this issue and is very easy to install once the existing floor slab is removed.

Radon gas is also an issue that we take seriously. We are not sure if we have significant or unhealthy radon levels, but it has been suggested that our basement ventilation system may effectively remove any radon gas.

After reviewing the EPA’s A Citizen’s Guide to Radon we decided that we are better off installing a proper radon removal system. Once the existing basement floor is removed it will be easy and cost effective to install – a good investment into our health.

Installing a new basement floor also allows us to resolve the heating issue by integrating a radiant floor system into the new concrete slab. That will make for a pretty comfortable basement – we hope. But it will require the rigid insulation under the slab/concrete floor. If not, the heat would draw into mother earth rather than the basement. And that would not help with the reduction of our carbon footprint.


Insulation – how much is needed?

We figured out that insulating the building from the inside with spray polyurethane foam (or, in short, spray foam) is the most suitable approach. It avoids potential conflicts with our masonry shell and will help with the moisture management in the brick walls.

The next question is: how much insulation do we need? We can look at it in terms of R-value (thermal resistance) or the depth of the spray foam layer, although both are somewhat proportionate to each other.

Here is what the building code says: R-49 for ceilings, R-19 for exterior walls and R-10 for basement foundations (Chicago Building Code, Chapter 18-13-102.1.1; Building thermal envelope insulation, Table 18-13-402.1.1). The Chicago Green Homes program requires R-52 for ceiling, R-21 for exterior walls and R-15 for basement foundations.

Having our eye on the zero-energy goal, it appears that more insulation or the highest possible thermal resistance is better. But there are limitations we have to wrestle with.

To keep the moisture management of the masonry shell intact, the whole interior wall assembly must have a perm rate of greater than 1. Closed cell spray foam has a better thermal resistance than open cell foam, but also lower perm rates. Limiting the closed cell foam to a 1 inch layer followed by open cell foam should yield the right perm rate and allow for the needed diffusion of water vapor through the wall assembly.

And then there is the space limitation. The building originally had no insulation. There was the outside masonry shell, a ¾ inch furring strip, followed by a ¾ inch wood lath and plaster assembly, which we removed.

Replacing the old 1 ½” interior wall assembly with 1 inch of closed cell foam plus dry wall, would only give us an R-value of around 6.5. Adding more insulation, beyond the 1 inch, would take away from the room size. Here are some scenarios:


My friend David Lemair knew about our effort to balance room size with R-value and pointed me to an article in Fine Homebuilding. I learned that spray polyurethane foam has a point of diminishing returns:

“… you would think that an R-40 wall full of spray foam would perform twice as well as a wall sprayed to R-20 with the same foam, but that is not the case.”

Source: Yagid, Rob; Spray Foam – What Do You Really Know?; Fine Homebuilding, June/July 2009

The article goes on to explain that the increased effectiveness from the R-20 to the R-40 wall is only about 2%. Open cell foam apparently reaches its point of diminishing return at 5 inches, closed cell foam already at 3 or 4 inches. No technical explanation is given to what causes that diminishing return, but I would really like to know!

The puzzle is coming together. We have determined that the closed cell foam must be limited to 1 inch to keep the perm rate greater than 1. It looks like open cell spray foam has its point of diminishing returns at 5 inches. That would give us a 6 inch insulation assembly with an R-value of about 24 that takes 4 ½ to 5 inches away from the room size. This is a good balance between R-value and room size.



Insulation – which material cuts it?

If you have followed the previous posts about the insulation conflicts and moisture management issues, you may ask why not go simple – skip insulation altogether and just have brick wall exposed on the inside. A very tempting thought, isn’t it? It would look pretty good and we could avoid all these problems.

But we also would create a big problem. A three wythe (or 12”) thick brick wall may have a R-4 value. The air film on the wall would give me another R-1, totaling R-5. That is if the brick is dry. If it is wet, these values will drop. A decent window may have a better R-value than the brick wall! We need good insulation, if we want to have a decent shot at our zero-energy goals.

There is quite a variety of materials to pick from, starting with the very common fiberglass batts, the more expensive rigid foam boards, or materials with high recycled content such as blown-in cellulose or recycled cotton batts.

Understanding the limitations and opportunities that come with our masonry shell, and having distilled two key principles, the choice actually narrows to just one material: blown-in foam insulation.

“A low[…] risk approach to interior masonry retrofits that has been used for several years involves spraying an airtight insulating foam directly to the back of the existing masonry [shell].”

Reference: Building Science Digest 114 (Interior Insulation Retrofits of Load-Bearing Masonry Walls in Cold Climates)

Also known as spray polyurethane foam (or in short: spray foam), it would eliminate air gaps and air leakage if applied across the entire interior shell, including the roof. Basically, it would give us an airtight building envelope and act as a moisture barrier (or vapor retarder) helping with the control of incidental rain penetration.

A Building Science publication (Building Science Digest 114) explains spray foam rationales and choice in detail and is worth while reading.

Because spray foam is semi-permeable (a vapor retarder but not a vapor barrier), it will allow moisture in the masonry shell to diffuse to the outside and in. I have to make sure that the perm rate of the entire interior wall assembly is greater than 1 – and we are all set!

There are two kinds of spray polyurethane foams out there:

Closed Cell

As the name suggests, each little cell (or bubble) encloses an air pocket, forming a monolithic airtight layer at an R-value of around 6.5 per inch. Most closed cell spray foams have a density of about 2 pounds per cubic foot (pcf) and have a low diffusion or perm rate (around 1 to 2 at 1 inch thickness).

Open Cell

This foam is much lighter at a density of 0.5 pcf and forms more of a web structure. It is still considered airtight if applied at a depth of several inches. The R-value for open cell products hovers around 3.5 per inch. Water vapor can diffuse freely through the material.

The one disadvantage of spray polyurethane foam that is often mentioned is cost. And yes, it is much more expensive than your typical fiberglass batts – closed cell more so than open cell, because it requires more material. Plus, it needs to be installed by a trained professional.

  • 6” of fiberglass batts (around R-19): $0.30 to $0.60 per square foot (material only)
  • 6”of open cell spray foam (around R-21): around $2.50 per square foot (material and labor)
  • 6”of closed cell spray foam (around R-39): $5.00 to $6.00 per square foot (material and labor)

We would pay more – and that is fine – because we will get more. With spray foam, we don’t have to worry about air leakage, condensation and potential mold problems, or diminished R-values. Instead, we get the airtight building envelope we need, and lasting R-values. If we would try to accomplish the same results with cheaper insulation materials, we probably would, in the end, pay as much.

A drawback that I still debate is that spray polyurethane foam is a petroleum based product. The good news is that most spray foams are now VOC (volatile organic compounds) free, using water as their blowing agent. Some products are marketed as green because of some soy based oil content. That overall content is, however, relatively small, plus I am not sure if I would accept soybean farming as a sustainable practice.

Another unanswered question that keeps me pondering has to do with the end-of-life use. There is no known recycling option or second use for this material. If the spray foam ever gets torn out, it is likely to end up in a landfill. The only conciliation I have is that it should serve and maintain its performance for several generations.

More info on spray foam:

What is:

Air barrier

Moisture barrier: See references below to vapor barrier and retarder.

Vapor barrier and vapor retarder

Additional resource: Consumer’s Guide to Vapor Barriers at the U.S. Department of Energy


Insulation – starts with moisture management

Following up on the previous post, common brick, like in our building, is very pervious to water. If adding insulation to a storage or mass wall system, such as our brick shell, one of the issues is condensation and potential freeze-thaw damage to the brick work. Insulation on the inside of the building can lead to condensation and interrupts the heat transfer into the masonry shell during the cold season. As such it is very likely that the shell will go through more freeze-thaw cycles than ever before.

“Freeze-thaw damage […] require the material to be at or near capillary saturation (100% Relative Humidity)”

Reference: Building Science Digest 138 (Moisture and Materials)

“Driving rain is typically the largest source of moisture for the above-grade building enclosure”

Reference: Building Science Digest 013 (Rain Control in Buildings)

The removal of water from our brick shell, or keeping the rain out, is – let’s say – rather important to its performance and integrity. It comes down to a balance of moisture storage capacity versus drying capacity. So, how does water or moisture move through a brick wall during wetting or drying?

I had to re-learn some basics of water and its various states (solid, liquid, vapor and adsorbed). The liquid and vapor states appear the most relevant. The former is pretty straight forward – or for that matter straight downward, controlled by gravity (water flows/drains downhill).

Good detailing can prevent rain from entering the storage or mass wall system and help with the balance between wetting and drying. This includes tuck pointing, drip edges, and the right flashing details, particularly around windows and in corners. Rain deflection through overhangs is another strategy.

“It should be clear that drainage is not sufficient for this purpose since it will leave large amount of saturated (100% Relative Humidity) material. Capillary and absorbed moisture can only be dried by evaporation followed by diffusion.”

Reference: Building Science Digest 138 (Moisture and Materials)

We are now talking about water vapor. Its movement is governed by three rules:

  1. Water vapor in the air moves from high pressure to low pressure areas.
  2. Water vapor diffuses through permeable materials from warm to cold.
  3. Water vapor diffuses through permeable materials from areas of higher concentrations to areas of lower concentrations.

As part of the drying mechanisms, I have to allow water vapor to diffuse out of the wall, whether towards the inside or outside.

In the summer, water in the brick tends to diffuse to the inside of the building, following the thermal and concentration gradient. Whatever kind of insulation system I decide to use, it is important that it allows for that inward driven moisture (water vapor) to pass.

“Rule Number One: Never install a vapor barrier on the inside of a wall assembly, which has a moisture reservoir cladding…”

Reference: Building Science Digest 108 (Investigating and Diagnosing Moisture Problems)

If moisture cannot pass, or if I add a vapor barrier to the interior wall assembly, summer moisture will condense in the wall assembly. That is a perfect recipe for water damage and mold growth – something our building has already seen in its past.

During winter, vapor tends to diffuse to the outside – again – along the thermal and concentration gradient. That vapor may have its origins in high Relative Humidity levels in the living spaces. The insulation I plan to add to the inside will reduce the temperature along the interior masonry shell. Inside air diffusing outwards and coming into contact with the cold masonry face could condense.

“Given sufficient air leakage and sufficiently high indoor Relative Humidity this condensate can accumulate faster than it can dry, and the interior face of the masonry will become saturated.”

Reference: Building Science Digest 114 (Interior Insulation Retrofits of Load-Bearing Masonry Walls in Cold Climates)

This in turn can create the potential for freeze-thaw damage.

Using insulation that can eliminate any air gap or air leakage with an airtight layer along the masonry shell should prevent condensation and subsequent freeze-thaw damage. But it still has to allow for vapor diffusion during summer (see above).

Confused? I don’t blame you! It took me a while to wrap my head around this. Eventually, I was able to boil it down to two key principles that I can use:

  1. The insulation will need to eliminate air gaps and needs to be air tight to eliminate air leakage driven condensation in the winter.
  2. The insulation will need to be permeable to water vapor for inward diffusion and drying during summer.